Recovery of uranium from seawater.

A computer program entitled URPE (Uranium Recovery Performance and Economics) has been developed to simulate the engineering performance and provide an economic analysis O of a plant recovering uranium from seawater. The conceptual system design used as the focal point for the more general AM analysis consists ofa floating oil-rig type platform, Asinlge-point moored in an open ocean current, using either high volume, low head, propeller pumps or the velocity head 4M of the ambient ocean current to force seawater through a mass transfer medium (hydrous titanium oxide (HTO) coated onto particle beds or stacked tubes), as in most process designs previously suggested for this service. Uranium is recovered Sfrom the seawater by an adsorption process, and later eluted . from the adsorber by an ammonium carbonate solution. A multi-product co-generating plant on board the platform burns coal to raise steam for electricity generation, desalination, and process heat requirements. Scrubbed stack gas from the plant is processed to recover carbon dioxide for chemical make-up needs.The equilibrium isotherm and the diffusion constant for the uranyl-HTO system, which are needed for bed performance calculations, have been calculated based on the rather sparse data reported in the literature. In addition, a technique for calculating the rate constant of a fixed bed adsorbing system has been developed for use with Thomas' solution for predicting fixed bed performance.The URPE program has been benchmarked against the results of previous studies by ORNL and Exxon, and found to make comparable performance and economic estimates when applied under the same set of ground rules. The URPE code was then used in an extensive series of parametric and sensitivity studies to identify optimum bed operating conditions and important areas for future research and development. The program showed that thin beds of small, thinly-coated particles were the preferred bed configuration, and that actively pumped systems out-perform current driven units.Based on the URPE analysis, the minimum expected costs nof uranium recovered from seawater would be no lower than ~316 (1979$)/lb U308 for state-of-the-art adsorber material (capacity equal to 210 mg U/kg Ti), but might be reduced to the level of breakeven attractiveness of ~150 (1979$)/lb U30 8 if at least a four-fold increase in adsorption capacity could be achieved. Specific research and development objectives other than increasing particle capacity are also indentified. Prospects are considered to be sufficiently good to warrant recommending further work

Systems studies on the extraction of uranium from seawater

This report summarizes the work done at MIT during FY 1981 on the overall system design of a uranium-from-seawater facility. It consists of a sequence of seven major chapters, each of which was originally prepared as a stand-alone internal progress report. These chapters trace the historical progression of the MIT effort, from an early concern with scoping calculations to define the practical boundaries of a design envelope, as constrained by elementary economic and energy balance considerations, through a parallel evaluation of actively-pumped and passive current-driven concepts, and thence to quantification of the features of a second generation system based on a shipboard-mounted, actively-pumped concept designed around the use of thin beds of powdered ion exchange resin supported by cloth fiber cylinders (similar to the baghouse flyash filters used on power station offgas).An assessment of the apparently inherent limitations of even thin settled-bed sorber media then led to selection of an expanded bed (in the form of an ion exchange "wool"), which would permit an order of magnitude increase in flow loading, as a desirable advance. Thus the final two chapters evaluate ways in which this approach could be implemented, and the resulting performance levels which could be attained. Overall, U 308 production costs under 200 $/lb appear to be within reach if a high capacity (several thousand ppm U) ion exchange wool can be developed

Raising Bi-O bands above the Fermi energy level of hole-doped Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} and other cuprate superconductors

The Fermi surface (FS) of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) predicted by band theory displays Bi-related pockets around the $(\pi,0)$ point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy ($E_F$) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole-doping the Bi-O bands drop below $E_F$ and the system self-dopes below a critical hole concentration. Computations on other Bi- as well as Tl- and Hg-based compounds indicate that lifting of the cation-derived band with hole doping is a general property of the electronic structures of the cuprates.Comment: 4 pages, 4 figures; PRL (2006, in press

Quantum Hall conductance of two-terminal graphene devices

Measurement and theory of the two-terminal conductance of monolayer and bilayer graphene in the quantum Hall regime are compared. We examine features of conductance as a function of gate voltage that allow monolayer, bilayer, and gapped samples to be distinguished, including N-shaped distortions of quantum Hall plateaus and conductance peaks and dips at the charge neutrality point. Generally good agreement is found between measurement and theory. Possible origins of discrepancies are discussed

Delayed neutron assay to test sorbers for uranium-from-seawater applications

Delayed Fission Neutron (DFN) assay has been applied to the measurement of uranium content in sorbers exposed to natural seawater for the purpose of evaluating advanced ion exchange resins. DFN assay was found to be particularly suitable for such testing because it is selective, nondestructive, yields quantitative results in the submicrogram range, and requires relatively simple sample preparation. Surplus components for a DFN system were obtained from the Lawrence Livermore National Laboratory, modified, re-assembled, and calibrated for use with M.I.T. irradiation facilities, following which procedures were developed, evaluated and applied to the experiments at hand.Four experimental ion exchange resins developed by the Rohm and Haas (R&H) Company specifically for uraniumfrom- seawater applications were evaluated, together with hydrous titanium oxide (HTO), the leading inorganic sorber for this purpose. Two types of tests using natural seawater were employed: batch loading experiments (paralleling similar tests done by R&H), and fixed-bed column loading experiments using a test facility at the Woods Hole Oceanographic Institute (WHOI). While some qualitatively consistent trends were evident among the various experiments, important quantitative inconsistencies were noted. The WHOI tests most closely approximated true in-service conditions; hence, more importance is assigned to these results.The MIT/WHOI tests confirmed 1.5 mm HTO particle bed uptake of approximately 300 ppm U for a 30 day exposure, in good agreement with the results reported by other laboratories, worldwide. An anion exchange resin employing an amidoxime functional group also achieved this level of performance, and, in addition, exhibited considerably superior mechanical properties. Moreover, the resin performance is expected to improve when its properties are optimized for the present application.U.S. Dept. of Energy

Languages and Learning at Key Stage 2: A Longitudinal Study Final Report

In 2006, The Open University, the University of Southampton and Canterbury Christ Church University were commissioned by the then Department for Education and Skills (DfES), now Department for Children, Schools and Families (DCSF) to conduct a three-year longitudinal study of languages learning at Key Stage 2 (KS2). The qualitative study was designed to explore provision, practice and developments over three school years between 2006/07 and 2008/09 in a sample of primary schools and explore children’s achievement in oracy and literacy, as well as the possible broader cross-curricular impact of languages learning